Theistic evolutionists: was Adam a specific person?

[juvenissun]

This doesn't make sense. Every generation has a 100 per cent death rate, and the following generation(s) carries on.



MANY "correct" mutations progressed into making us human.

How many? Thousands? Are all these correct ones have the same effect? If not, how many of them have the same effect? Ten? or Hundred?

 

[sfs]

Why would that happen? Is mutation supposed to be random under any condition? If A mutated one way, why should B mutated the same way (or have a better chance to mutate the same way)? Would that have a very very small chance?

It doesn't happen because the same mutation happens again. It happens because people (and other species) pass the mutation on to their children. My father, like every father, had ~75 new mutations when he was born -- that is, 75 places where his DNA was different than the DNA of either of his parents. He passed his DNA on to my brother and me, so he passed on those mutations -- those different bits of DNA.

But passing on DNA is a crapshoot. Like everyone, my father had two copies of each chromosome, so for each of the 75 places where his DNA had changed, he had a 50% chance of passing on the mutated version and a 50% chance of passing on the unmutated version. For some of those 75 mutations, my brother and I each got the mutated copy, for others only one of us did, and for others neither did. So when my father was born, each of the 75 had one copy in the population. Today, some of them have two copies, some one and some zero. In short, the frequency of the mutations changed from one generation to the next, purely because of chance.

The same process will go on every generation. In the next generation, some of the 75 have 3 copies, some 2, some 1 and some 0. And it's going on in everyone else in the populations too. Some genetic variants (which is what mutations are) become more frequent, some less frequent. Eventually some of them reach 100% in the population, and no more change is possible, at least until another mutation occurs at the same site.

 

[Willtor]

In fact, you don't even need natural selection. All you need is that some mutations will increase in frequency over time, which happens by chance even when no selection is occurring ("genetic drift"). That's undoubtedly why most of the genetic differences between humans and chimpanzees are there.

Genetic Drift is an important observation. Most of the significant phenotypical differences probably involve natural selection, but if you're only looking at the genome (which the creationists seem to be doing) it's certainly true that most differences can be accounted for by randomness alone. It's probably true even in coding DNA where the third base in a codon tends not to have a lot of impact on the protein.

 

[dad]

My father, like every father, had ~75 new mutations when he was born -- that is, 75 places where his DNA was different than the DNA of either of his parents. He passed his DNA on to my brother and me, so he passed on those mutations -- those different bits of DNA.

But passing on DNA is a crapshoot.

Is it really though? The choices we make determine a lot about how our bodies are. If sin affected a person in certain ways, could that could result, perhaps, in what we might call a mutation? I mean, what could cause DNA not to copy properly? What external influences might some sins result in? How about gene flow or migration? I could see how repeated sins of some types might result in stuff migrating between people...!?

Science might see it all as random, but that may simply reflect the small minded scope or perspective they are all about.

 

[juvenissun]

It doesn't happen because the same mutation happens again. It happens because people (and other species) pass the mutation on to their children. My father, like every father, had ~75 new mutations when he was born -- that is, 75 places where his DNA was different than the DNA of either of his parents. He passed his DNA on to my brother and me, so he passed on those mutations -- those different bits of DNA.

But passing on DNA is a crapshoot. Like everyone, my father had two copies of each chromosome, so for each of the 75 places where his DNA had changed, he had a 50% chance of passing on the mutated version and a 50% chance of passing on the unmutated version. For some of those 75 mutations, my brother and I each got the mutated copy, for others only one of us did, and for others neither did. So when my father was born, each of the 75 had one copy in the population. Today, some of them have two copies, some one and some zero. In short, the frequency of the mutations changed from one generation to the next, purely because of chance.

The same process will go on every generation. In the next generation, some of the 75 have 3 copies, some 2, some 1 and some 0. And it's going on in everyone else in the populations too. Some genetic variants (which is what mutations are) become more frequent, some less frequent. Eventually some of them reach 100% in the population, and no more change is possible, at least until another mutation occurs at the same site.

Thanks for the patience. But I still do not understand the idea of "frequency".

The mutations passed to you from your father would be totally different from the mutations you passed to your child. Right? Because the same mutation seldom or never repeats itself (right?).

According to what you said, the above understanding must be wrong. But why? What is the chance to have two DNA mutated exactly the same way?

 

[sfs]

Thanks for the patience. But I still do not understand the idea of "frequency".

The mutations passed to you from your father would be totally different from the mutations you passed to your child. Right? Because the same mutation seldom or never repeats itself (right?).

In this usage, "mutation" means the changed DNA. If my grandfather passed on a C at position 1,146,298 of chromosome 6, but in my father that mutated to a G, then the G was now at a frequency of 1 copy (out of all the copies in the population). If he passed on the G to both of his sons, then the frequency increased to 2. If he only passed it on to one of us, then it's still at a frequency of 1.

It doesn't have to mutate again; the changed base can be passed on and on.

 

[juvenissun]

In this usage, "mutation" means the changed DNA. If my grandfather passed on a C at position 1,146,298 of chromosome 6, but in my father that mutated to a G, then the G was now at a frequency of 1 copy (out of all the copies in the population). If he passed on the G to both of his sons, then the frequency increased to 2. If he only passed it on to one of us, then it's still at a frequency of 1.

It doesn't have to mutate again; the changed base can be passed on and on.

Thanks.

So, father A passed the mutation x to son A, it counted the frequency as 1.
And father B passed the mutation x to son B, then it is counted as 2.
etc.
The larger the population, the higher possible frequency of mutation x.
Correct?

Does it mean this special type of mutation is a "good" mutation which fits the environment better? What is the chance to have both father A and father B to have exactly the same mutation x? It is very very small, right?

 

[Willtor]

Thanks.

So, father A passed the mutation x to son A, it counted the frequency as 1.
And father B passed the mutation x to son B, then it is counted as 2.
etc.
The larger the population, the higher possible frequency of mutation x.
Correct?

In an absolute sense, yes. But one typically sees frequencies measured in percentages of the population rather than absolute numbers.

Does it mean this special type of mutation is a "good" mutation which fits the environment better? What is the chance to have both father A and father B to have exactly the same mutation x? It is very very small, right?

It doesn't necessarily mean the mutation was "good." Rather than thinking in absolute "good" and "bad" it's useful to think in terms of the probability that an organism with the mutation will survive to reproduce, versus an organism without the mutation. This is an essential point in talking about the practicalities of evolution:

Think of two grandmasters playing chess. You might think that Kasparov is better than Karpov. But that doesn't mean that Kasparov always wins. When we say he's better, we mean that the probability that he wins is greater than 0.5.

It's the same with the mutations. When there is a mutation, one wants to determine whether the change will contribute to the likelihood that the organism will reproduce. Now, even with a slightly bad mutation, there is the possibility that the organism will reproduce (Karpov may beat Kasparov), but over the course of generations, the version of the genome with the higher likelihood will have a higher frequency.

There _are_, also, neutral mutations that don't alter any of the probabilities.

---

The probability that father A and father B independently get the same mutation is very small. But if they have a common ancestor, it's much more likely. If grandfather C (father of A and B) had the mutation, depending on where the mutation occurred, A and B are almost guaranteed to have the mutation, too.

But if no common ancestor had the mutation, A and B are unlikely both to have it.

 

[juvenissun]

In an absolute sense, yes. But one typically sees frequencies measured in percentages of the population rather than absolute numbers

...

The probability that father A and father B independently get the same mutation is very small. But if they have a common ancestor, it's much more likely. If grandfather C (father of A and B) had the mutation, depending on where the mutation occurred, A and B are almost guaranteed to have the mutation, too.

But if no common ancestor had the mutation, A and B are unlikely both to have it.

That is exactly where my question is at.

If grandfather C passed mutation_x to father A and father B, then the frequency of mutation_x would be 2. But if son A also get mutation x from father A, it would NOT be counted as another increment of mutation_x. At the same time, other people in the population are NOT likely to have mutation_x. So, the "frequency" of mutation_x will be difficult to pass even 10. In this example, the frequency of mutation_x would be 2, forever (assume C has only two children, A and B). The effect of mutation_x may stay with offsprings of Grandfather C, but the frequency will not increase any more.

If so, how can anyone count the frequency of ANY particular mutation by the percentage of a population?

 

[sfs]

That is exactly where my question is at.

If grandfather C passed mutation_x to father A and father B, then the frequency of mutation_x would be 2. But if son A also get mutation x from father A, it would NOT be counted as another increment of mutation_x. At the same time, other people in the population are NOT likely to have mutation_x. So, the "frequency" of mutation_x will be difficult to pass even 10. In this example, the frequency of mutation_x would be 2, forever (assume C has only two children, A and B). The effect of mutation_x may stay with offsprings of Grandfather C, but the frequency will not increase any more.

As usual, I have difficulty figuring out what you're trying to say. Forget other people having the same mutation -- just assume it happened only once. You were okay with there being two copies of the mutated DNA, in two different people. Good. To make things simple, we'll assume that everyone has exactly two children, so that the population stays the same size -- call it 10,000 people.

So each of the two people with the mutated DNA has two children. Each one can pass the changed DNA to 0, 1, or 2 of their children. That means in the next generation there can be anywhere from 0 to 4 copies. In the generation after that, there can be anywhere from 0 to 8 copies. Wait long enough, and there will be anywhere from 0 to 20,000 (2 copies per person) copies of the mutation.

If at any point, the number of copies reaches zero, then that mutation is lost from the population. If at any point, the number of copies reaches 20,000, then it has reached fixation and it can't change in frequency anymore (at least no unless there's a new mutation).

 

[juvenissun]

As usual, I have difficulty figuring out what you're trying to say. Forget other people having the same mutation -- just assume it happened only once. You were okay with there being two copies of the mutated DNA, in two different people. Good. To make things simple, we'll assume that everyone has exactly two children, so that the population stays the same size -- call it 10,000 people.

So each of the two people with the mutated DNA has two children. Each one can pass the changed DNA to 0, 1, or 2 of their children. That means in the next generation there can be anywhere from 0 to 4 copies. In the generation after that, there can be anywhere from 0 to 8 copies. Wait long enough, and there will be anywhere from 0 to 20,000 (2 copies per person) copies of the mutation.

If at any point, the number of copies reaches zero, then that mutation is lost from the population. If at any point, the number of copies reaches 20,000, then it has reached fixation and it can't change in frequency anymore (at least no unless there's a new mutation).

Thanks again. I do understand what you explained.

If so, I think the word "frequency" is a misused term. It is not frequency, but is simply a count, an accumulated sum over generations, on the feature caused by a particular mutation since it took place. Once it happened, it will have a count. It will never be zero. If the effect, the consequence, stayed, then the count, the "frequency", will only become higher and higher.

For example: It started with 1, then the next generation (two children) has between 0 and 2. If it became 0, then the total count is still 1. If the third generation have 0 to 8. And if it was 1 >0 >1, then the total is 2. If in the fourth generation it became 10, that is: 1>0>1>10 (possible?), then the total (the frequency) becomes 12. And the "frequency" of that particular mutation at the time of fourth generation will be expressed as 12/(current population(?)). (If it is the current population, but not the original population, then the frequency in % could become lower and lower. Right?)

Do I get it this time?

 

[Willtor]

Thanks again. I do understand what you explained.

If so, I think the word "frequency" is a misused term. It is not frequency, but is simply a count, an accumulated sum over generations, on the feature caused by a particular mutation since it took place. Once it happened, it will have a count. It will never be zero. If the effect, the consequence, stayed, then the count, the "frequency", will only become higher and higher.

For example: It started with 1, then the next generation (two children) has between 0 and 2. If it became 0, then the total count is still 1. If the third generation have 0 to 8. And if it was 1 >0 >1, then the total is 2. If in the fourth generation it became 10, that is: 1>0>1>10 (possible?), then the total (the frequency) becomes 12. And the "frequency" of that particular mutation at the time of fourth generation will be expressed as 12/(current population(?)). (If it is the current population, but not the original population, then the frequency in % could become lower and lower. Right?)

Do I get it this time?

Eventually, organisms start dying. If the first generation organism died before having any offspring, or if its offspring didn't have the variant, the frequency goes to zero. So it isn't monotonically increasing.

Additionally, in your example, if the second generation didn't get the allele, then none of their children got it, either. The 0-8 number comes from the range of possibilities without knowing anything about the individual generations, except that each has 2 children. Once you pin down a number (the first generation doesn't pass on the allele, in your example), the range gets reduced (0, in your example).

 

[Paul of Eugene OR]

How many? Thousands? Are all these correct ones have the same effect? If not, how many of them have the same effect? Ten? or Hundred?

Thousands, and bear in mind even members of the same species are not genetically identical

 

[sfs]

If so, I think the word "frequency" is a misused term. It is not frequency, but is simply a count, an accumulated sum over generations, on the feature caused by a particular mutation since it took place.

No, it's the count in the current generation. That number can increase and decrease. (As for the use of the word "frequency", you can convert from the count I gave to the fraction of the population by dividing by the number of chromosomes in the population, 20,000 in this case. That's in fact the way geneticists usually report variant frequencies. As if happens, though, statisticians will tell both the geneticists and you that you're using the word incorrectly: for them, "frequency" is a count, not a fraction.)

Otherwise, what Willtor said.

 

[juvenissun]

No, it's the count in the current generation. That number can increase and decrease. (As for the use of the word "frequency", you can convert from the count I gave to the fraction of the population by dividing by the number of chromosomes in the population, 20,000 in this case. That's in fact the way geneticists usually report variant frequencies. As if happens, though, statisticians will tell both the geneticists and you that you're using the word incorrectly: for them, "frequency" is a count, not a fraction.)

Otherwise, what Willtor said.

Thanks to all.

Now, an example: If we have 50 white tigers among 5000 tigers today, does that mean the frequency of the "white tiger mutation" is 1% today?

 

[sfs]

Thanks to all.

Now, an example: If we have 50 white tigers among 5000 tigers today, does that mean the frequency of the "white tiger mutation" is 1% today?

Probably not. It's a little more complicated than that because each tiger (and each person) has two copies of every chromosome. If the white tiger mutation is dominant, so that they only need one copy of it to look white, then the frequency is 50/10000 = 0.5%. (If it's recessive, the mutation's frequency is around 10%, since 10% squared is 1%.)

 

[juvenissun]

Probably not. It's a little more complicated than that because each tiger (and each person) has two copies of every chromosome. If the white tiger mutation is dominant, so that they only need one copy of it to look white, then the frequency is 50/10000 = 0.5%. (If it's recessive, the mutation's frequency is around 10%, since 10% squared is 1%.)

OK, let me make it more realistic and goes back toward the OP.

Do you think a white tiger (or other similar cases) is a result of mutation of a single DNA, or is a combined result of bunch of mutations?

My point is: If it is a product of multiple mutations, would the chance of duplicating the same mutations on other individuals (no blood-line link) becomes nearly zero?

 

[sfs]

OK, let me make it more realistic and goes back toward the OP.

Do you think a white tiger (or other similar cases) is a result of mutation of a single DNA, or is a combined result of bunch of mutations?

My point is: If it is a product of multiple mutations, would the chance of duplicating the same mutations on other individuals (no blood-line link) becomes nearly zero?

In the case of white tigers, it is a single mutation. But take a real case like skin pigmentation in humans. Lighter skin has been selected for as humans have moved away from the tropics, and multiple mutations in multiple genes have spread in the population. In fact, different genes were involved in Asia and in Europe (with some overlap).

In this kind of situation, there's no reason at all that the same mutation would have to occur in different individuals. (Sometimes it does happen, e.g. the sickle cell mutation has occurred multiple times, as has the mutation conferring lactose tolerance.) Instead, one person has one mutation that makes skin somewhat lighter. That's selected for and spreads in his descendants. Someone else, at a different time, has a different mutation in another gene that also makes skin somewhat lighter. That one spreads through her descendants. Eventually, some individuals inherit both new variants, and their skin is even lighter and their descendants do even better than those with the single mutation.

 

[Willtor]

...

My point is: If it is a product of multiple mutations, would the chance of duplicating the same mutations on other individuals (no blood-line link) becomes nearly zero?

In the general case, yes, it's pretty unlikely* and you'd have to work pretty hard to exclude the possibility that there was a common ancestor with the variant. You could imagine two men with a particular SNP (Single Nucleotide Polymorphism: a single letter change) on the Y chromosome, and you'd figure they had a common ancestor with the change.

But if their Y chromosomes otherwise look like they belong to different lineages, besides the SNP, then it's more likely the mutation happened twice because saying that it happened once means that there were a lot of other mutations that happened twice, in exactly the same places.

* -- I don't want to say "nearly zero" as the probability of any specific mutation is "nearly zero." Geneticists tend to work with log probabilities (where you take the logarithm of the probabilities and compare those numbers) because the numbers they are comparing are so tiny (also, other reasons that are not relevant, here).

It would be better for you to say, "it is less likely, in the general case, that the same mutation happened twice in two different people than that they share a common ancestor with the mutation."

 

[juvenissun]

m

In the general case, yes, it's pretty unlikely* and you'd have to work pretty hard to exclude the possibility that there was a common ancestor with the variant. You could imagine two men with a particular SNP (Single Nucleotide Polymorphism: a single letter change) on the Y chromosome, and you'd figure they had a common ancestor with the change.

But if their Y chromosomes otherwise look like they belong to different lineages, besides the SNP, then it's more likely the mutation happened twice because saying that it happened once means that there were a lot of other mutations that happened twice, in exactly the same places.

* -- I don't want to say "nearly zero" as the probability of any specific mutation is "nearly zero." Geneticists tend to work with log probabilities (where you take the logarithm of the probabilities and compare those numbers) because the numbers they are comparing are so tiny (also, other reasons that are not relevant, here).

It would be better for you to say, "it is less likely, in the general case, that the same mutation happened twice in two different people than that they share a common ancestor with the mutation."

I don't care how people use log scale to shrink the apparent value of number, the fact is it is a big number, and it means the chance is not only "less likely", but is very very unlikely. The emphasis must be given.

If so, why do we have a number of cases of white tiger, but zero case of red tiger green tiger or black tiger? I would think a green tiger is even more environmentally advantageous.

Now, back to the old question: Why should "Adam" represent a large number of humans, rather than a single human? I don't see a reason for that from the genetic (mutation) point of view.